Rotax 912 uls shakes violently

Leif Westin wrote:

Hi all, I'll be back when I find the error

Best

Leif Westin

Just remember - it seems to be a human trait, that we go for the most complex & costly solution first, when logically, we should start with the simplest least costly.

As mentioned previously, please check the carburetor floats have not sunk!

Hello Have changed the gearbox temporarily. Problems gone. A slight vibration at 4600-4800rpm. Will also order a new propeller, found damage on the leading edge. So now it's time to renovate the gearbox.

Thanks for all the support

Hi Leif,

Congratulations for solving (finding?) the problem.

One thing more: Check the type of the spark plugs.Vibrations causes from a running engine. Vibrations can hurt all parts of the engine, including the gear box. Renovate the gear box is surely good but is the gear box really the origin of your problem? If problems occur at special times or events and then they dissapear sometimes, in my oppinion this could not be causes by a static part. For me a gear box is mostly a static part even if there are some gear wheels running. Defects at the gear wheels are mostly shown by a noise first. My experiance is that the combustions by the running engine is the beginning of vibrations and this is not to avoid. But abnormal vibrations can caused by abnormal combustions.

You checked some parts of the line like carburator (including the carburator floats?), ignition and so on, did you checked the spark plugs?. Are the NGK installed?  - an easy question - easy to check An another easy thing. My experience with the carburator vent hose shows that this can be a big influence at the carburator. Are the carburator vent hoses fixed in a right position maybe like at the beginning? Much more easier to check-  So from some contributers mentioned before start with the first and easiest to find the origin of your problem.

Greetings

Hi Leif,
and a small addendum: the spark plug connector and the cables also belong to the spark plugs. Is there possibly a contact problem which occurs when the speed is changed or the temperature rises? Violent shaking also occurs when a spark plug fails or premature ignition occurs when the plugs are carbonized. You changed the ignition boxes, did you also change the cables and plugs? Contact problems can occur sporadically, which does not make troubleshooting easy.
If you make changes to an engine, like changing the gearbox or something else then it can easily happen that other components are touched and the fault disappears. But the change was not the cause even though you think that is the proof of the cause. It is possible that the error will occur again later.

Greetings